1. Field of the Invention
The present invention relates to reaction cured glass and glass coatings which exhibit high resistance to elevated temperatures and thermal shock which are prepared by reacting a mixture of glasses including a porous high silica borosilicate glass such as Vycor 7930 described in U.S. Pat. No. 2,286,275 and boron oxide with at least one intermetallic or metallic substance selected from a group of compounds consisting of silicon tetraboride, silicon hexaboride, other boron silicides, boron and mixtures thereof.
The reaction cured glass composites of the present invention are particularly useful as thin glazed coatings for porous silica structures such as silica reuseable surface insulation (RSI) a low density porous fibrous rigid insulation and foamed silica in applications at temperatures from -100.degree. C (-150.degree. F) to 1482.degree. C (2700.degree. F). The glassy composites may also be used to form reaction vessels and tubing capable of operating at temperatures around 1260.degree. C (2300.degree. F) while withstanding repeated heating and cooling and thermal shock.
The glassy composites and coatings of the present invention are stable towards devitrification and exhibit good mechanical properties to temperatures in excess of 1092.degree. C (2000.degree. F). The coatings and articles made in accordance with the invention exhibit low thermal expansion coefficients and consequently a high resistance to thermal shock and are of high purity and can provide surfaces with high opacity and emittance, or if desired have transparent or translucent surfaces.
Reaction cured glass coatings in accordance with the invention provide a useful system for coating reuseable surface insulation (RSI) and other porous ceramic bodies. The coated body will exhibit high surface emittance, good resistance to thermal shock, and is inert to air or vacuum environment. The coatings of the invention do not cause excessive shrinkage or distortion of the substrate and do not devitrify or cause devitrification of a silica substrate material even at temperatures around 1260.degree. C (2300.degree. F).